TAXON
24(I): 53-66. FEBRUARY
1975
EVOLUTION OF GRASSESAND GRASSLANDS
IN SOUTH AMERICA
Arturo Burkart*
Summary
This is a discussion of the South American grasslands from the standpoint of their
evolution and composition. The tribes are considered in relation to climate, and grasses
are classified as mega-, meso-, or microthermic with respect to their temperature
requirements. The principal grassland regions are three: (A) Tropical and Subtropical,
which include the Llanos of the Orinoco River system and the Campos Cerrados of
Central Brazil; (B) Temperate, including the Pampa of Argentina and the Campos of
Uruguay; and (C) Cold Country Grasslands, which are the Steppes of the high Andes
and Patagonia, and also the Pairamos of Colombia and Ecuador. Some attention is given
to the floristic composition of each of these regions. The subject of endemism is dealt
with, as well as the problem of disjunct distribution. Included is a discussion of changes
brought about by agriculture and ranching in historic times, and what may be expected
in the future.
INTRODUCTION
The Gramineae, with about 6oo genera and some 6ooo species, is one of
the largest families of flowering plants. It is a truly cosmopolitan group,
and remarkable because of the capacity of its members to form the dominant vegetation over large areas of the earth's surface. The terms steppes,
savannas, prairies, pusztas, campos or pampas all refer to vegetation types
in which grasses are dominant. To quote Ronald Good (1953; p. 53)
"Pride of place must certainly go to the Gramineae . . ., the great family ...
Not only do the grasses reach to the furthest land in the north and to the
borders of Antarctica in the south, but their degree of distribution is
usually particularly complete and continuous. Almost alone among the
families of flowering plants they form the dominant element in vegetation
over great areas of the world, and nearly everywhere else too, except
perhaps in some forest regions, the proportion of these plants is high."
South America, as we shall see, is no exception, having rich and extensive
grasslands. If we include both pure and mixed types, savanna or parkland,
this subcontinent possesses nearly 3,500,000 square kilometers of grassland.
Approximately a quarter of its entire area is, or was originally, natural
grassland (with, of course, many herbaceous dicotyledons and members of
other groups associated). In the other vegetation types: Tropical Rainforests, Subtropical Forests or Woods, Pairamos, Puna, Catingas, Chaco,
Monte, and Deserts or Semi-deserts, grasses are well represented, but not
dominant. An exception is, however, the Bambuseae, which are very
conspicuous in hot humid or mountainous forest regions, and even in the
* Instituto de Botinica Darwinion, Lavarden
Buenos Aires, Argentina.
FEBRUARY
1975
0oo, Correo Martinez, San Isidro, prov.
53
humid temperate forests of south-central Chile (Parodi, 1945).
Along with the Leguminosae, Rosaceae, Vitaceae, Solanaceae, Cruciferae,
and Cucurbitaceae, the Gramineae are closely connected with history, prehistory, and the development of human civilization. Long before man
appeared on earth, grasslands must have played a decisive role in the
evolution of such important and diversified animals as the ruminants,
equidae, and other herbivores - mainly in the Old World. In South
America, grasslands developed extensively without supporting large herds
of vertebrate herbivores - except perhaps during the Tertiary, with great
extinct mammals - up to the time of the Spanish and Portuguese conquests.
The influence of prehistoric man also was very limited. The natural grasslands of South America are, therefore, a nearly undisturbed result of the
great biological processes: evolution, competition, and migration, since their
origins in the second half of the Mesozoic. During the entire Tertiary
period, i.e. some 6o,000,000 years or more, the development of the grasslands was governed by the principal environmental factors: climate, geology, soils, topography, and diverse biological influences (parasites, pollinators, symbionts, etc.).
In spite of the great number of publications devoted to grasses, innumerable questions posed by the morphology, taxonomy, genetics, cytology,
anatomy, embryology, physiology, ecology, etc., of these plants are still
unanswered. They inspired Agnes Arber's (1934) admirable book, "The
Gramineae;" a work of timeless value. Modern grass systematics has
changed substantially the schemes of Nees, J. C. Doell, Bentham & Hooker,
E. Hackel, and A. S. Hitchcock, superseding the classifications based purely
upon exomorphology and inflorescence characters. It exemplifies the highest development of an integrated or synthetic taxonomy, being a model not
yet attained in other families. The modern system for the Gramineae (cf.
Potztal in Melchior, Engler's Syllabus ed. 12. 1964) is the result of a
combined effort of workers in the special fields mentioned above, and
makes use of basic contributions by authors such as: N. P. Avdulov, R. J.
Roshevitz, H. Prat, J. R. Reeder, L. R. Parodi, F. A. McClure, G. L.
Stebbins, T. Tateoka, and others.
New lines of research are developing, as for example the recent discovery
of a number of entomophilous olyroid grasses in the tropical rain forest of
northern South America (Soderstrom & Calderon, 1971). This changes the
traditional picture of grasses which were thought always to be wind
pollinated, and, moreover, breaks down the no less traditional concept of
a correlation between petaliferous, showy flowers, with zoophily against
perianth reduced "amentiferous" flowers and anemophily. Electron microscopy, applied to plastids, pollen, and other cell structures, is able also to
contribute substantially to a deeper understanding of the natural affinities
or diversities.
PHYLOGENY AND TAXONOMY OF THE GRASS FAMILY
With respect to origins, we may focus on the main processes of evolution: mutation, hybridization, introgression, chromosome changes - the
domain of genetics, the science of heredity and variation. Or we may seek
to describe the actual historical developments and connections by which
the different taxonomic groups of grasses (i.e. tribes, genera, species) originated from extinct progenitors. This is properly phylogeny, but to arrive
54
TAXON
VOLUME 24
at meaningful conclusions, we need a fairly complete fossil record.
Unfortunately, this is not the case in the Gramineae. The oldest remains
are dated, with doubt, as Jurassic (Bambusidium liasicum Heer; Poacites (?),
according to Roshevitz, 1969). Several fossils are considered to be
Cretaceous, and they include some genera recognized as present-day
Arundo, Phragmites, Bambusa (Gothan & Weyland, 1954). Two conclusions seem warranted: (I) the grass family appeared simultaneously with
the early Angiosperms during the Cretaceous evolutionary explosion, and
their development and migration dates back to early and middle
(2)
Tertiary times (Oligocene, Miocene, etc.). It continued vigorously during
the Quaternary. From this later period, Roshevitz (1969) mentions many
well known genera: Arundinaria, Setaria, Oryzopsis, Phragmites, Bromus,
Festuca, Agropyron, Hordeum, Alopecurus, and Beckmannia. At the present
time, however, paleontology has not revealed the multiple steps in the phylogeny of the different grass groups. Even so, it is perhaps significant that
the few earliest grass fossils, which have been identified with certainty, belong to tribes or subfamilies considered primitive by modern agrostologists:
Phragmitoideae (Arundo, Phragmites) and Bambusoideae (Bambusa, Chusquea).
In South America, several grass fossils have been identified. Menendez in
Fittkau et al. (1969) reported Poacites from the Cretaceous, and Parodi &
Frenguelli (1941) described a fossil bamboo of the genus Chusquea from
Chubut. Such remains demonstrate the very old and independent development of the grasses in our subcontinent. But again, the fossil record is so
meagre that it is of slight help in reconstruction of the phylogenetic events.
It remains for us, therefore, to utilize the indirect but classical method,
for the construction of an acceptable phylogeny of the grass family. We
must rely on comparative morphology in its broad sense, including anatomy, dermatography, palynology, embryology, as well as cytogenetics,
ecology, and phytochemistry, in our attempt to discover the natural
affinities. To venture a "genealogical tree" is a risky enterprise, but I think
the possibilities in this case are equal or better than in any other plant
group. Roshevitz (I946, cf. translation, 1969) gives an interesting picture
of grass phylogeny, beginning with the primitive Streptochaeteae and other
tribes of the subfamily Bambusoideae. The ancestors of Gramineae can
perhaps be defined as Proto-Commelinales (Farinosae, pro parte), especially
from pre-Restionaceous and Flagellariaceous stock. Roshevitz' conceptions,
revolutionary at the time, are still valid in the main lines, e.g., the primitiveness of "Phragmitiformes", (now Phragmitoideae) is generally considered to be a connecting link between Bambuseae and the three (now
four) great, more modern and herbaceous groups, at present called Pooideae
(Festucoideae), Eragrostoideae ("Eragrostiformes") and Panicoideae ("Paniciformes"). From the latter I prefer to separate as a parallel, perfectly
equivalent group, the Andropogonoideae (Tribes Andropogoneae, Maydeae,
and probably Arthropogoneae), founded by R. Pilger and E. Potztal.
The characters of leaf anatomy and karyology led to the foundation of
the intermediate subfamilies Phragmitoideae and Eragrostoideae, formerly
included in the Pooideae, based on their gross morphology. These are
indeed new concepts which connect the widely separated Pooideae with the
Panicoideae and Andropogonoideae, which are at present, the most numerous and widespread Gramineae of the world.
Time does not permit a more detailed discussion of the new and very
FEBRUARY
I975 5J
5
natural system of the Gramineae (Parodi,
I96I). I would stress, however,
that it is founded on such a high degree of correlation of different
characters, that there seems little doubt of the correctness of the conclusions.
GRASSGROUPS
MEGA-, MESO- AND MICROTHERMIC
I come now to the interesting relation between natural tribes and
climate. With our new delimitations of subfamilies and tribes, there is such
a close agreement between temperature requirements or preferences of
their members, that climatic factors can be used as a component of the
diagnosis.
The basic influence of temperature on vegetation led Alphonse De
Candolle to formulate the distinction between mega-, meso-, and microthermic plants (1874, cited by C. Troll,
Roshevitz wrote in 1946 (translation1935).
1969, p. io): "Finally we must
note that the subfamily Pooideae is common in temperate and cold zones,
while the subfamily Panicoideae [including the Andropogonoideael is typical of tropical countries."
Hartley (i95o), as a result of a statistical study, reported that the main
tribes of Gramineae show a high correlation to a particular geographical
area, either tropical or cold to temperate, being above normal in numbers
in their own climatic area, or below normal in the other areas. By normal
he refers to the percentage of the total grass flora.
In my work on the grasses of the Argentine province of Entre Rios
(Burkart, 1969), I adopted this order for the tribes because I think it serves
admirably to characterize areas, especially if combined with hydric preferences (hydrophilous, hygrophilous, mesophilous, xerophilous).
Rosengurtt, et al. (1970) group the Uruguayan grass tribes into those of
"winter cycle" and "summer cycle." As Uruguay lies in the mesothermic
area, this allows them to distinguish the two groups of micro- and
megathermic origins.
I. Megathermic groups: from equatorial and tropical areas with 200C or
more mean annual temperature, and over I5OC mean winter temperature.
In South America, the equatorial and tropical vegetational zones are
most extensive in the lowlands, mesetas, and lower sierras, between ca. 13W
northern and nearly 280 southern latitude. But the Cordillera de los Andes
is a formidable barrier which alters the climate through altitude, with
profound influence on vegetation. In the Tropical Andes, the megathermics
reach ca. I 5oo m, the mesothermics 15oo-35oo m, and microthermics ca.
m elevation, often reaching the line of perpetual snow.
3500-5000
Under tropical or subtropical, i.e. megathermic conditions, which prevail
over three-fourths of the South America's surface, the temperature factor
loses importance and hydric conditions control the phases of vegetation.
This is especially true in the savannas (llanos, campos cerrados, palmares).
There is a wet season ("invierno") which produces a great development
of grasses; and a dry season ("verano") which marks a maturation, seeding,
and dispersal of the plants. Whith more general rainfall, where forests do
not thrive, a continuous herb and grass flora flourishes the year round.
Nearly the whole of Brazil, the Guayanas and Venezuela, Paraguay and
Northern Argentina, as well as the extra-Andean parts of Bolivia, Peru,
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TAXON
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24
Ecuador, and Colombia have this type of vegetation. The grass tribes here
exclusive or dominant are:
Streptochaeteae (forests); Bambuseae (forests, along rivers, humid mountains); Olyreae (forest understory); Oryzeae (swamps); Paniceae (forests,
savannas, swamps, dunes); Andropogoneae (campos, savannas, swamps,
etc.); Arthropogoneae; Maydeae; Arundinelleae (campos); Eragrosteae
(campos); Chlorideae (campos); Aristideae (campos).
II. Mesothermic groups: these are intermediate in temperature requirements, and grow mainly in areas with io-200C mean annual temperature
OC mean winter temperature. The following tribes, in whole or in
and 5-I5
are
part,
representative: Bambuseae (Chusquea-South Central Chile and
Argentina); Arundineae (Arundo, Cortaderia); Aveneae; Agrosteae; Triticeae; Phalarideae; Danthonieae; Pappophoreae; Meliceae; Sporoboleae;
Stipeae; Chlorideae; Eragrosteae; Aristideae; Paniceae; Andropogoneae.
Conditions for these mesothermic grasses prevail in the temperate zone
in large areas of central Argentina, Chile, all of Uruguay, and the extreme
south of Brazil (Rio Grande do Sul), between roughly 280 and 400 south
latitude. Because of the Cordillera's influence, the zonation is much distorted from the northwest to the southeast. Rainfall diminishes steadily
from east (I200-900 mm per year) to the west, where semi-desert conditions prevail (5oo-Ioo mm per year). Here the grasslands disappear and
are replaced by the xerophilous, shrubby "monte" vegetation.
The principal grassland of this zone is the Pampa, covering more than a
half million square kilometers of plains, with a steppe character in the
drier west, and prairie physiognomy in the east. To the north, the Gran
Chaco has much grassland between woods and palm groves. The same is
true for the Argentine Mesopotamia (Entre Rios, Corrientes) and part of
the extensive Campos of Uruguay and Rio Grande do Sul, altogether
another half million square kilometers of land.
Winter and Summer Phases in the Mesothermic Grassland Zone.
The natural Pampas and Uruguayan Campos consist of a mixture of
originally megathermic and microthermic grasses. The former are plants
which flower in summer and autumn; the latter flower in spring, seeding
in early summer. In various parts of the year, therefore, the Pampa
presents very different aspects. In spring (September-November) the dominants are Poa, Bromus, Stipa, Briza, Piptochaetium, Hordeum, and Calamagrostis; in summer (January-March) representatives of the following
genera are in flower: Paspalum, Panicum, Bothriochloa, Schizachyrium,
Digitaria, Setaria, Chloris, and Eragrostis. Many Paniceae, Andropogoneae,
Chlorideae, and Eragrosteae of megathermic, neotropical origin are represented by numerous adapted species. The mild winters with temperatures
seldom falling below o0C permit them to complete their life cycles. Therefore, during the summer and autumn the vegetation has a subtropical
aspect. Conversely, other mesothermic grasses of microthermic affinities
find the winter temperature favorable for vegetative growth, and after
flowering and seeding in the spring pass the hot season in a more or less
dormant stage.
In the annual species, this difference is even more pronounced, and we
have two kinds of these grasses in the temperate zone, which extend farther
FEBRUARY
1975
57
from their original home than the perennials, except for some weedy ones:
WINTER ANNUALS
SUMMERANNUALS
Poa annua
Vulpia sp.
Koeleria phleoides
Digitaria sanguinalis
Setaria viridis
Setaria verticillata
Eragrostis pilosa
Eragrostis virescens
Aristida adscensionis
Loliummultiflorum
Hordeummurinum
Hordeum euclaston
Soil conditions or exposure may alter the general scheme. In Entre Rios,
near the subtropical boundary, on the high shores of the Uruguay River, I
found Andropogoneae flowering in spring (September), which is exceptionally early. In South Brazil, on the "campinas altas" or in humid forests,
some species or the micro- or mesothermic genera (Bromus, Poa, Festuca,
Stipa) flower during the summer.
III. Microthermic groups: from cold temperate or cold climates, with less
than IooC mean annual temperature and less than 5OC mean winter
temperature.
Members of the following tribes, with a predominance of those belonging
to the Festuceae, are to be found here. It will be noted that with the exception of the Arundineae, all belong to the subfamily Festucoideae: Arundineae, Festuceae, Triticeae, Aveneae, Agrosteae, Stipeae, Phalarideae.
The distribution of these grasses is restricted in tropical and subtropical
South America to the high Cordillera, at a considerable altitude above sea
level. At more southern latitudes they are to be found in the phytogeographical provinces called Andina, Chilena Central, Patagonica, and
Subantarctica, with considerable transgressions into the neighboring Monte,
Pampa, and even Uruguayan provinces (winter/spring vegetation). Only in
South Patagonia, with lower temperatures, owing to latitude, do they
form grasslands down to sea level. The dominants are species of Festuca,
Poa, Bromus, and Stipa, with admixtures of Hordeum, Hierochloe,
Trisetum, Deschampsia, Agropyron, Elymus, Agrostis, Alopecurus, Polypogon, Phleum, and other cold-climate, mostly widespread genera
(Soriano, 1956; Parodi, 1941, 1949; Dimitri, 1972). In Patagonia, natural
grasslands occur only in the restricted sections in which aridity is not
extreme, mainly in the Subandean, Western, and Fuegian districts.
The genus Stipa plays an outstanding role in South American meso- and
microthermic grasslands, and is absent in the megathermic ones. With some
80ospecies in our subcontinent, Stipa is one of the largest grass genera, and
is especially important because of having developed many xerophilous
species, adapted to the prevailingly arid conditions in western mountainous
and southern temperate regions.
THE THREE MAIN GRASSLAND
DOMINIONS
OF SOUTH
AMERICA
In accordance with the preceding climatic groupings of South American
grass tribes and genera, and somewhat independent of current geobotanical
subdivisions, we may now proceed to enumerate and to mark the limits of
the main grass regions (see map):
A. Tropical and SubtropicalGrasslands.This vegetation is of the savanna type
58
TAXON
VOLUME 24
No. 103
SOUTH AMERICA
80
70
60
so
40
ILI
P,
oi
0
1
0
0
o0
M
oo
7nrc
20
o~jrI0
- - - - - - - - ---- ----- ---I
20
-- - --- --
--------
- --------
..
0
o.*
.......
. ...
,SCAL
ul1
'50
r
t
09
0
rerd
?L
0
0
0
2
0 WSTLOGIUD
Map i. South America's main vegetational divisions and grassland regions.
FEBRUARY
1975
59
and is dominated by megathermic grasses with a variable admixture of woody
plants, shrubs, trees, or palms, which never form dense groves.
1) The Llanos of the Orinoco River system in Colombia and Venezuela.
2) The Campos Cerrados of Central Brazil, when of the more open type.
3) The Swamp grasslands with hydrophilous or swimming grasses (such as
Hymenachne amplexicaulis, Panicum elephantipes, and Paspalum repens); the
Marajd Island area at the mouth of the Amazon; the Gran Pantanal in Matto
Grosso, where the Paraguay River has its sources, and the Delta of the Parana'
(Burkart, 1957).
4) The South Brazilian Campos, northern parts, including the humid lower
Campinhas or small grasslands surrounded by the forest, mainly with acid soils.
5) The Tropical and Subtropical East-Andean Grasslands, which extend on a
narrow tract at medium altitudes on the humid eastern slopes of the Andes, above
timberline, from Venezuela and Colombia to Bolivia and northwestern Argentina.
Everywhere in this domain there is strong competition between woody plants,
tending to the natural forest climax, and grasses and herbs, which build up the
savanna. Climatic or edaphic conditions have determined the existence of savannas. Grasses are better adapted to a long dry period than are trees, and the
latter require better and deeper soils. Through human activities (grazing, burning,
etc.) the natural savannas have been extended, favoring the grasses, and forests
are becoming more and more restricted.
B. Temperate Grasslands. This is the dominion of the mesothermic grass groups.
Geographically, they occupy much of the vast plains between the western bushlands and the Atlantic Coast in Argentina and Uraguay. Ecologically, these plains
seem to be an inmense ecotone where typical grasslands developed with genera
and species of mixed origin: mega- and microthermics. Many species are endemic.
This domain includes the La Plata River grasslands, composed of two regions:
1) The Pampa (sometimes called the Humid Pampa, to exclude the Monte
bushlands), in the main Argentine provinces of Buenos Aires, eastern La Pampa,
and southern parts of C6rdoba, Santa Fe, and Entre Rios provinces.
2) The Campos of Uruguay and southern Rio Grande do Sul.
Together these constitute one of the richest regions in the world for Gramineae.
Fortunately, this grass flora is now fairly well known. In recent years three
Floras have appeared: Burkart, 1969; Rosengurtt, Maffei, & Izaguirre, 1970;
Cabrera, 1971. These cover Entre Rios, Uruguay, and Buenos Aires, respectively.
The number of different species growing wild or naturalized in the three
territories is 553, many of which are common to the different political divisions.
C. Cold Country Grasslands. A region of microthermic Gramineae, which
embraces from north to south the whole extension of the subcontinent, but in the
tropics only a narrow strip at high altitude on the Andean chain:
1) The Paramos of Venezuela, Colombia and Ecuador, with Espeletia (Compositae) dominating. This high altitude, cold, and humid formation is not properly
grassland, but is rich in Gramineae.
2) The high Andean Mountain Steppes of Peru, Bolivia, and northwestern
Argentina.
3) The Patagonian-Fuegian-Falkland Steppe, mainly in the subandean districts.
FLORISTIC
COMPOSITION
OF THE THREE GRASSLAND
TYPES
The specific composition of the different grasslands, according to authors
who have studied them, confirms the theory of temperature preferences of
tribes and genera. Within each of the climatic zones, the presence of forest
or grasslands (under conditions not disturbed by man) depends more on
rainfall quantity and distribution, or on edaphic factors, than on temperature.
60
TAXON
VOLUME 24
Megathermics:
Los Llanos (Venezuela and Colombia).
A typical example of neotropical savannas.Mean Annual temperature27.50 C; annual
variation ca. 2.5OC. Rainfall 800-i200 mm mean per year.
Principal dominant Gramineae (cf. Luces, 1942; Blydenstein, i962; Velasquez, 1965).
Figures following the generic names indicate the number of species when more than one.
Oryzeae: Leersia, Luziola, Oryza (2).
Arundineae:Cortaderia (3), Gynerium.
Eragrosteae:Eragrostis(5).
Chlorideae:Bouteloua (2), Chloris (3), Gymnopogon(2), Leptochloa,Trichloris(2).
Sporoboleae:Sporobolus(5).
Pappophoreae:Pappophorum.
Zoysieae: Aegopogon (2), Tragus.
Aristideae:Aristida (4).
Paniceae: Anthephora,Axonopus (3), Brachiaria,Cenchrus,Digitaria (2), Echinochloa,
Echinolaena, Eriochloa (2), Homolepis, Hymenachne, Isachne, Leptocoryphium,
Mesosetum(2), Oplismenus,Panicum (3), Paspalum (6), Pennisetum, Reimarochloa,
Setaria (4), Thrasya.
Arundinelleae:Arundinella (2).
Andropogoneae: Andropogon (4), Diectomis, Elyonurus (2), Erianthus, Eriochrysis,
Heteropogon, Hyparrhenia (2), Imperata, Sorghastrum,Trachypogon(4).
Maydeae: Tripsacum.
The Campos Cerrados (Central Brazil). Savannas.
Brazil, occupying nearly one-half of the land surface of South America, has
a rich grass flora which is still imperfectly known. The only attempt at a
comprehensive treatment of the Gramineae is that of Doell in Martius' Flora
Brasiliensis (1871-1878), which is badly out of date. Forests are extensive and
varied, but through human influence - agriculture, grazing, and burning - many
areas have been converted to artificial or seminatural grasslands. The original
grass formations in Brazil extend over parts of the territory of Mato Grosso,
Minas Gerais, Sao Paulo and Goias, but they are of the savanna type with trees,
palms, or small woods interspersed. Modern authors (cf. Ferri, 1973) consider
that many campos left without human influences revert to secondary natural
forest after some 30 or 40 years.
The grass flora is very rich, and therefore it is impossible to give here a list of
species. The dominance of Andropogoneae and Paniceae is very apparent. Species
of Panicum and Paspalum are very abundant, and more than 20 other genera
of Paniceae occur in this region.
Several African grasses are cultivated for forage and have become established:
Melinis minutiflora, "capim melado"; Hyparrhenia rufa, "yaragui", Panicum
maximum, "guinea" or "coloniao; Brachiaria mutica, "Pari", Rhynchelytrum
repens, "capim natal", Pennisetum clandestinum, "kikuyu," etc. These naturalized
exotics demonstrate ecological affinities between Brazil and tropical Africa.
Moreover, there are floristic similarities, mainly on the generic level (JacquesFelix, 1962).
Guayana Highland Savannas
These differ from Llanos in being tableland of up to 1000 m altitude and of
very old geological structure. The grass flora is still poorly known. (cf. Lemee,
1955).
Mesothermics:
The large temperate plains grassland regions, Argentine Pampa and UruguayanSouth Brazilian Campos.
FEBRUARY
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61
1. There are many descriptions of the Argentine Pampa grasslands. Parodi
(1930) published the fi'rst comprehensive study on the more northern sector,
enumerating 110 grass species, native and naturalized. He was aware of the
seasonal cycle which I have already discussed. Cabrera (1971) describes 374
species of Gramineae for the entire province of Buenos Aires.
A large proportion of these extremely complex natural prairies of the Pampa
except in stony or very low soils have been destroyed through agriculture. Even
in 1920-1930, Dr. Parodi had difficulty in locating examples in the virgin state.
Due to the richness of the soil, the humid Pampa is the most productive agricultural land in Argentina. Today in these areas, one can travel for miles and see
only fields of cereals, alfalfa, or European weeds. Natural reserves are the
mountainous enclaves in southern Buenos Aires province, called by geologists
Ventania and Tandilia (Sierras de la Ventana and Sierras de Tandil). Here a
rich native grass flora persists, with the addition of endemics such as Poa iridifolia
Hauman and Bromus bonariensis L. R. Parodi & Camara. Farther south we find
tussock-grass steppes with Stipa brachychaeta Godron dominating. To the northeast, the depression of the Rio Salado, recently described by F. Vervoorst (1967),
has a natural grass cover of Distichlis spicata (L.) Greene and D. scoparia (Kunth)
Arech. In these areas, plowing is not feasible but overgrazing has heavily affected
these grasslands.
Microthermics:
The Cordillera and precordillera region along the Patagonian Andes is an important zone for the study of the struggle, during recent geological periods,
between forest (the Nothofagus communities) and steppe (mainly Festuca grasslands). Through pollen analysis and other data it has been possible to demonstrate
in Magallanes, Chile, that the steppe during the Pleistocene extended farther west,
where today there is only Nothofagus forest.
Where humidity is sufficient or irrigation possible, all of the best forage grasses
of central and northern Europe grow well and are being established for the
improvement of agriculture.
In the high Andes of western Venezuela (cf. Luces, 1942), common genera are:
Aciachne, Agrostis, Bromus, Calamagrostis, Cinna, Danthonia, Festuca, Helleria,
Hierochlo?, Poa, Stipa, and Trisetum.
In Ecuador, Peru, and Bolivia, also in the high Andes with moderate humidity,
(cf. Hitchcock, 1927; Tovar, 1957), common genera are: Aciachne, Agropyron,
Agrostis, Alopecurus, Anthochloa, Briza, Bromus, Calamagrostis, Danthonia,
Dissanthelium, Elymus, Festuca, Hordeum, Muhlenbergia, Nassella, Poa, Stipa,
Triniochloa, and Trisetum.
Another region includes Patagonia, Fuegia, and the Southernmost Islands.
According to Boelcke (1957), Soriano (1956), and Roig (1964), the majority of
species are members of the following genera: Agropyron, Agrostis, Alopecurus,
Bromus, Cortaderia, Danthonia, Deschampsia, Distichlis, Elymus, Festuca, Glyceria,
Hierochlo,, Hordeum, Koeleria, Phleum, Poa, Polypogon, Stipa, Trisetum, and
Vulpia.
GRASS GENERA ENDEMIC TO SOUTH AMERICA*
There are relatively few grass genera endemic to South America, most of
them being common to two or more continents. Notwithstanding
this fact,
the endemic genera indicate that South America may be a very old center
for the origin of Gramineae. The number of endemic species, however, is
* I acknowledge the generoushelp of the Argentine agrostologist,Dra. Elisa Nicora, in
preparingthis list.
62
TAXON
VOLUME 24
rather large. This suggests that the process of speciation has been very
active for long geologic periods within our subcontinent.
Aciachne Bentham, high tropical Andes, Venezuela to Bolivia and Nw Argentina.
A. pulvinata Benth. Tribe: Stipeae.
Agenium Nees, South Brazil, Paraguay, Bolivia, and Argentina. One species: A.
villosum (Nees) Pilger. Tribe: Andropogoneae.
Anthaenanthiopsis Mez ex Pilger, Paraguay, Bolivia, Northern Argentina (Misiones,
Jujuy). 4 species in diverse habitats. Tribe: Paniceae.
Chusquea Kunth, humid forests, mainly tropics but also in the Patagonian Cordillera
of Chile and Argentina, to Lake Buenos Aires (460 S. Lat.) in cold humid climate.
C. culeou E. Desv. Tribe: Bambuseae.
Erianthecium L. R. Parodi, known only from Uruguay, on hills and stony campos. One
species: E. bulbosum L. R. Parodi. Tribe: Festuceae.
Guadua Kunth, forests and riversides of tropical regions. Tribes: Bambuseae.
Hemimunroa (L. R. Parodi) L. R. Parodi, Chile, Puna de Atacama, Bolivia, and
adjoining Argentina, on arid sandy stony soils. One species with one variety: H.
andina (Phil.) L. R. Parodi and var. breviseta (Hack.) L. R. Parodi. Tribe:
Eragrosteae.
Lamprothyrsus Pilger, 3 species in Argentina; 2 in Peru and Bolivia. Tribe: Danthonieae.
Lorenzochloa J. & C. Reeder, one species: L. erectifolia (Swallen) J. & C. Reeder in
the high Andes of Venezuela, Colombia, and Peru. Tribe: Stipeae.
Merostachys Spreng., several species. Tribe: Bambuseae.
Nassella E. Desv., Andean genus of ca. 9 species in Ecuador, Peru, Bolivia, Chile, and
Argentina; most species in Chile. Tribe: Stipeae.
Neobouteloua Gould, one species: N. lophostachya (Griseb.) Gould, in west central
Argentina (Tucuman to Mendoza), and Chile. Tribe: Chlorideae.
Oplismenopsis L. R. Parodi, one species: 0. najada (Hack. & Arech.) L. R. Parodi,
Rio de la Plata region. Tribe: Paniceae.
Otachyrium Nees, mainly Brazil, several species, one in Argentina. Tribe: Paniceae.
Relchela Steud., Chile and western Patagonia in Argentina. One species: R. panicoides
Steud. Tribe: Festuceae.
BOREAL INFLUENCES IN THE GRAMINEAE OF SOUTH AMERICA
The megathermic tribes and genera of grasses in this subcontinent show
evident affinities with the paleotropical groups of Africa (cf. Jacques-Felix,
1962), which suggests a possible ancient land connection.
If the Gramineae developed in the Mesozoic, as fossil remains seem to
prove, the present distribution of so many nearly cosmopolitan genera in
both the New and the Old World, is best explained by Alfred Wegener's
classic theory of Continental drift, now modernized and accepted by most
geologists. From the original stock, which was already considerably diversified, the present grass flora developed during the Tertiary and Quartenary.
This resulted in more localized species both to the north and to the south
of the equator.
Long distance migration is another possible explanation for the similar-
ities of the flora of South and North America,and even with Eurasia.
In fact, what seem to be boreal influences along the Andes Cordillera,
are very evident in the tribes classified as micro- or mesothermic in the
present paper. Temperate or cold slopes and valleys along the Andes, at
medium or high altitudes, allowed many genera the sort of migration
sometimes called "mountain hopping." Whether this process proceeded
only from north to south, and not inversely, is hard to say. For instance,
Stipa, Festuca, Poa, Calamagrostis, Hordeum, and other genera probably
FEBRUARY
1975
63
of holarctic origin, developed very important secondary centers of polymorphism in western and southern South America. The Andes may have
been the indispensable migration bridge. Some examples are given below:
GRAMINEAE
WITH DISJUNCT AREAS: UNITED
STATES AND ARGENTINA
a) Disjunct Genera
MonanthochloW Engelm. Two halophilous species, one in North America: M. littoralis
Engelm., surrounding the Gulf of Mexico and in California; the other M. acerosa (Griseb.)
Speg., in central Argentina, surrounding the Salinas Grandes, a remnant of an ancient
epicontinental sea, and down to San Luis province.
Blepharidachne Hackel. Two species in the United States: B. kingii (S. Wats.) Hack.
in Nevada and California, and B. bigelovii (S. Wats.) Hack. in Texas. B. benthamiana
(Hack.) Hitchc. in Argentina (Mendoza, San Luis).
Munroa Torrey. Four species: M. squarrosa (Nutt.) Torr., Rocky Mountains to Texas;
M. decumbens Phil., Puna region in S Peru, N Chile, SW Bolivia, and NW Argentina.
M. argentina Gris. and M. mendocina Phil. in NW and W central Argentina.
Tridens Roem. & Schult. Fourteen species in the United States and Mexico; two in
Brazil and eastern Argentina: T. brasiliensis Nees ex Steud. and T. hackelii (Arech.) L. R.
Parodi.
Erioneuron Nash. Five species in the United States and Mexico. In western Argentina
2 species with 5 varieties: E. pilosum (Buckl.) Nash and E. avenaceum (H.B.K.) Tateoka
(Jujuy to Rio Negro).
Scleropogon Phil. Monotypic: S. brevifolius Phil. Southwestern United States, northern
and central Mexico; Argentina: arid zones of the Precordillera in Mendoza and San
Juan Provinces.
b) Disjunct Species
Phalaris angusta Nees. United States: Mississippi, Louisiana, Texas, California. Brasil,
Chile, and Argentina: Buenos Aires, Entre Rios, Rio Negro.
Muhlenbergia torreyi (Kunth) Hitchc. United States: Kansas and Colorado to Texas
and Arizona. Argentina: Cordoba, San Luis, La Pampa. Also in Mexico and Puerto Rico.
Sporobolus cryptandrus (Torr.) A. Gray (= S. subinclusus R. A. Phil.). United States
and Northern Mexico. Argentina: Mendoza, Cordoba, San Luis, La Pampa, Buenos Aires,
and Rio Negro.
Deschampsia atropurpurea (Wahl.) Scheele. Greenland, Labrador, Alaska, United States
(Colorado, California). Argentina: from Neuquen southwards to the Magellan Strait.
Habitat: alpine, humid prairies in cold regions of both hemispheres.
Deschampsia flexuosa (L.) Trin. Greenland to Alaska; Eurasia; United States. Argentina: Patagonia to the Islas Malvinas (Falkland Islands).
Deschampsia caespitosa (L.) Beauv. Greenland to Alaska; United States. Argentina:
along the southern Cordillera, Mendoza to Punta Arenas (not to Fuegia). An Arctic and
antarctic cosmopolite.
Deschampsia elongata (Hook.) Munro ex Benth. Western North America, Alaska, to
Mexico. Andes of Chile and Argentina: Neuquen to Santa Cruz.
Calamagrostis (Deyeuxia) neglecta (Ehrh.) Gaertn., Meyer, & Schreb. Eurasia, North
America. Argentina, southern Andes, Rio Negro to Tierra del Fuego.
Willkommia texana Hitchc. The var. texana endemic in Texas. In Argentina, prov.
Buenos Aires, the var. stolonifera L. R. Parodi.
Stipa speciosa Trin. & Rupr. California: Chile, semideserts in the North; Argentina:
Patagonia.
Bouteloua aristidoides (H.B.K.) Griseb. United States and Mexico, in the arid regions
of the West: western Argentina.
Bouteloua barbata Lag. United States, arid West, and Mexico; western Argentina.
Trichloris crinita (Lag.) L. R. Parodi (= T. mendocina (Phil.) Kurtz). North America:
Texas, Arizona, and Mexico; northwestern Argentina, western Chaco, very common and
important for recovery of pastures in the arid zone.
64
TAXON
VOLUME 24
Panicum urvilleanum Kunth. Typical psammophyte with long creeping rhizomes, in
semiarid habitats: Southern California; Peru, Chile, western and central Argentina.
Eriochloa gracilis (Fourn.) Hitchc. Southern United States and Mexico. Argentina:
Cordoba, Salinas Grandes.
Setaria leucopila (Scribn. & Merr.) K. Schum. Southwestern United States and Mexico.
Argentina: southwestern C6rdoba, eastern La Pampa and southwestern Buenos Aires
provinces.
Finally, "Grasses and Grasslands in South America" is a fascinating research field,
and much is yet to be done. No doubt there are still unknown species to be discovered
and described. Much can be learned concerning the evolution and relationships of the
various genera and species. Our present knowledge of the ecology of tropical and
subtropical grasslands is scanty, as is information which will permit us to determine, in
many cases whether the vegetation is primary or secondary. The Gramineae are, indeed,
an extremely successful group. In South America, as in other parts of the world, representatives are to be found in nearly every plant community.
Acknowledgement
I thank Prof. John R. Reeder for his interest and for his critical reading of my
manuscript.
References
ARBER, AGNES 1934 - The Gramineae. A Study of Cereal, Bamboo, and Grass. Reprinted
in 1965 by J. Cramer, Weinheim. [With Introduction by W. D. Clayton, pp. i-xxxii.]
J. 1962 - La Sabana de Trachypogondel Alto Llano. Estudio ecol6gico de
la regi6n alrededor de Calabozo, Estado Guirico. Boletin Soc. Venezolana Cienc.
Natur. 23: 139-206.
BOELCKE, O. 1957 - Comunidades herbiceas del norte de Patagonia y sus relaciones con
la ganaderia. Revista Invest. Agricolas (Buenos Aires) 11: 5-98.
BURKART, A. 1957 - Ojeada sin6ptica sobre la vegetaci6n del Delta del Rio Parana.
Darwiniana 11(3): 457-561.
BURKART, A. 1969 - Flora Ilustrada de Entre Rios. Vol. 2. Gramineas. Buenos Aires:
Instituto Nacional de Tecnologia Agropecuaria.
CABRERA, A. L. 1970 - Flora de la Provincia de Buenos Aires. Parte II, Gramineas.
Buenos Aires: Instituto Nacional de Tecnologia Agropecuaria.
DIMITRI, M. J. 1972 - La Regi6n de los Bosques Andino-Patag6nicos. Sinopsis General.
Buenos Aires: Instituto Nacional de Tecnologia Agropecuaria. (cf. Genera of the
Andean-Patagonia Gramineae, pp. 243-248.)
DOELL, J. C. 1871-1878 - Gramineae. Vol. 2, pt. 2. 1871, and Vol. 2, pt. 3, 1878. In:
Martius, K. F. P. & A. G. Eichler, Flora Brasiliensis. Miinchen.
FERRI, M. 1973 - Sobre a origem, a manten•ao e a transforma?-o dos Cerrados. Ecologia
BLYDENSTEIN,
I(i): 5-10.
GooD, RONALD1964 - The Geography of Flowering Plants. Ed. 3. New York.
GOTHAN,W. & H. WEYLAND 1954 - Lehrbuch der Paleobotanik. Berlin.
HARTLEY, W. 95o0 - The global distribution of the tribes of Gramineae. Australian J.
Agric. Res. 1: 355-373HITCHCOCK, A. S. 1927 - The grasses of Ecuador, Peru, and Bolivia. Contr. U. S. Nat.
Herb. 24(8): 291-556.
JACQUES-FELIX, H. 1962 - Les Graminees d'Afrique Tropicale. Paris: Institut Recherches
Agronom. Tropicales.
LEMtE, A. 1955 - Flora de la Guyane Frangaise, I. Paris. (cf. Gramineae, pp. 83-161.)
LUCES,ZORAIDA1942 - Generos de las Gramineas Venezolanas. Boletin Tecnico Minist.
Agric. Cria 4: 1-152.
MENENDEZ, C. A. 1969 - Die fossilen Floren Siidamerikas. pp. 519-561. In: Fittkau, E. J.,
J. Illies, H. Klinge, G. H. Schwabe, & H. Sioli, Biogeography and Ecology in South
America. II. The Hague: W. Junk.
FEBRUARY 1975
65
L. R. 1930 - Ensayo fitogeografico sobre el partido de Pergamino. Revista Fac.
Agron. y Veter. Univ. Nac. Buenos Aires 7: 65-271.
PARODI, L. R. 1941 - Revisi6n de las Gramineas sudamericanas del genero Hierochloe.
Revista Mus. La Plata n.s. 3 (Bot. 14): 183-212.
PARODI, L. R. 1945 - Sinopsis de las Gramineas chilenas del genero Chusquea. Revista
Universitaria, Univ. Cat6lica de Chile 30(I): 61-71.
PARODI, L. R. 1949 - Las Gramineas sudamericanas del genero Deschampsia. Darwiniana
8(4): 415-475. (Resume in Lilloa 17: 289-302.)
PARODI, L. R. I96I - La taxonomia de las Gramineas Argentinas a la luz de las investigaciones mis recientes. Recent Advances in Botany (IX Internat. Bot. Congress,
Montreal, 1959) I: 125-I30.
PARODI, L. R. & J. FRENGUELLI 1941 - Una Chusquea f6sil de El Mirador (Chubut).
Notas Mus. La Plata Paleontolog. 6(32): 235-238.
POTZTAL, EVA 1964 - Graminales. Vol. 2, pp. 561-579. In: Melchior, H. (Editor), A.
Engler's Syllabus der Pflanzenfamilien. Ed. 12.
RoIG, F. A. 1964 - Las gramineas mendocinas del genero Stipa. I Taxonomia. Revista
Fac. Cienc. Agrarias Univ. Nac. Cuyo, Mendoza, Argentina
i1: 3-11o.
ROSHEVITZ, R. J. 1969 - Evoluc.o e sistemitica das Gramineas. Boletim Inst. Bot. S.o
Paulo 5: 1-20. [Translation from Russian by Tatiana Sendulsky of the 1946 paper.]
IZAGUIRRE
DE ARTUCIO,
DE MAFFEI& PRIMAVERA
ROSENGURTT,
B., BLANCAARRILLAGA
1970 - Gramineas Uruguayas. Universidad Publicaciones (Univ. de la Republica,
Montevideo, Uruguay).
SODERSTROM, T. R. & CLEOFi E. CALDER6N 1971 - Insect pollination in tropical rain
forest grasses. Biotropica 3(I): 1-16.
SORIANO, A. 1956 - Los distritos floristicos de la Provincia Patag6nica. Revista Invest.
Agricolas (Buenos Aires) io: 323-347.
TOVAR S., O. 1957 - Las Gramineas de Huancavelica. Primera Parte. Mem. Museo Hist.
Nat. "Javier Prado" 6: -0iio.
TROLL,C. 1935 - Gedanken und Bemerkungen zur oekologischen Pflanzengeographie.
Geogr. Z. 41(10): 380-388.
VELAZQUEZ,
J. 1965 - Estudio fitosociologico acerca de los pastizales de las sabanas de
Calabozo, Estado Guarico. Boletin Soc. Venezolana Cienc. Natur. 26(109): 59-IOI.
VERVOORST, F. 1967 - La Vegetaci6n de la R. Argentina, VII. Las Comunidades
Vegetales de la Depresi6n del Salado (Prov. de Buenos Aires). Serie Fitogeogrifica,
Instit. Nac. de Tecnologia Agropecuaria, 7: 1-262, 44 lIminas, I mapa.
PARODI,
66
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